GB966811A - Improvements in or relating to the preparation of crystalline semi-conductors - Google Patents

Abstract

In a process for depositing Si layers on a parent crystal of Si by disproportionation of the di-iodide to give the tetra iodide and Si, the ratio of SiI4 to SiI2 in the reaction gas is restored to its original value after each deposition stage by passing the reaction gas over Si at a higher temperature than the deposition temperature. In the Figure a gas (preferably inert such as A or N2) is passed in at E it picks up iodine J which is led to vessel B where it reacts with the silicon G to give a SiI4SiI2 mixture at a temperature of 1000-1100 DEG C. This mixture is then passed to vessel C where Si is deposited on parent crystals K, which are at a temperature of 700-800 DEG C. The SiI4SiI2 ratio is then restored to its original value by passing the depleted mixture into vessel D and contacting it with more silicon G preferably at the same temperature <PICT:0966811/C1/1> as in vessel B, the temperature in the second deposition chamber F preferably being the same as in chamber C. The process can be repeated as many times as desired and improvements described consist in having parallel circuits and/or circulatory gas flow. Prior to starting the process the apparatus is evacuated or flushed with an inert oxygen free gas to remove all traces of air and water vapour. Suitable doping agents can be included in the reaction mixture. When hydrogen is present in the gas mixture the regeneration temperature is lower (e.g. 100-200 DEG C. lower) than the separation temperature, e.g. 900-1100 DEG C.ALSO:<PICT:0966811/C6-C7/1> In a process for depositing Ge layers on a parent crystal of Ge by disproportionation of the di-iodide to give the tetraiodide and Ge, the ratio of GeI4 to GeI2 in the reaction gas is restored to its original value after each deposition stage by passing the reaction gas over Ge at a higher temperature than the deposition temperature. In the Figure, a gas (preferably inert such as N2 or A) is passed in at E, it picks up iodine J which is led to vessel B where it reacts with the germanium G to give a GeI4-GeI2 mixture at a temperature of 500-800 DEG C. This mixture is then passed to vessel C where Ge is deposited on parent crystal K1 which are at a temperature of 400-430 DEG C. The GeI4-GeI2 ratio is then restored to its original value by passing the depleted mixture into vessel D and contacting it with more germanium G preferably at the same temperature (500-800 DEG C.) as in vessel B. The temperature in the second deposition chamber F is preferably the same as in chamber C i.e. 400-430 DEG C. The process can be repeated as many times as desired, and improvements described consist in having parallel cricuits and/or circulating gas flow. Prior to starting the process the apparatus is evacuated or flushed with an inert oxygen-free gas to remove all traces of air and water vapour. Suitable doping agents can be included in the reaction mixture. When hydrogen is present in the gas mixture the regeneration temperature is lower (100-200 DEG C. lower) than the separation temperature (e.g. 700-900 DEG C.).